A coupling device for fluid transfer is known in the art that is used for transferring liquid such as a chemical solution between a container of a delivery truck and a storage tank (see Patent Japanese Unexamined Patent Application, Publication No. Hei 8-296782, for example).
In the coupling device disclosed in Japanese Unexamined Patent Application, Publication No. Hei 8-296782, a bellows holder, a bellows integrated with the bellows holder, and a shower ring are pressed by air pressure against a plug attached to a flexible tube, with the plug fitted inside the coupling device, so that fluid supplied through the flexible tube is allowed to move into the bellows. After the liquid transfer operation, the bellows holder, the bellows integrated with the bellows holder, and the shower ring are returned to their original position by air pressure to close a distal opening of the plug.